The present invention relates generally to the production of bent sheets or plates of glass and, more particularly, to an improved gravity mold apparatus for use in bending glass sheets to relatively sharp angles.
In some of the latest automotive designs, it has been found desirable to provide certain of the glazing closures, such as the backlights for example, with sharp bends to form a central panel portion extending continuously across the vehicle from one side to the other thereof, and integral end portions sharply bent inwardly relative to the central panel portion about generally vertical lines to extend longitudinally into the sides of the vehicle.
One successful technique developed for imparting such sharp bends to glass sheets is disclosed in U.S. Pat. Nos. 3,762,903 and 3,762,904, assigned to the same assignee as the present invention, whereby one or more electrically conducting paths are formed on at least one surface of the glass sheet along the line or lines about which it is desired to sharply bend the sheet. The sheet is then supported on a suitable gravity mold structure and heated in a furnace to a temperature corresponding to the softening point of the glass, causing it to sag by gravity into conformance with the shaping surfaces of the mold while simultaneously passing electric current through the electrically conducting path or paths to heat the area of the glass sheet immediately adjacent said paths to a temperature above the aforementioned softening point, causing the sheet to bend along such path or paths to form the desired relatively sharp bends therein.
In order to supply electric current to these paths, the molds are provided with electrically conducting means including bus bars adjacent one end thereof adapted to be engaged by electrically conducting probes projecting into the path of the bus bars as they advance with the mold through the furnace. More recently developed molds are provided with three bus bars mounted on the frame and which must be electrically insulated therefrom to preclude shorting-out of the circuitry. This has been accomplished in known molds by bolting each bus bar at a plurality of spaced points to the mold frame and providing individual insulators in the form of flanged bushings for each bolt fastener arrangement. While such known mold assemblies have served the purposes for which they were intended, they possess certain disadvantages. For example, when damaged, it is often necessary to remove the bus bars for repair and/or replacement or to gain access to other damaged mold components. Since the typical mold assembly is provided with 18 bolt connections for the three bus bars, removal and reassembly thereof becomes an arduous and time consuming task, adding materially to production costs. Also, because of the small mass and fragility of each insulator, they are easily chipped, fractured and even dislodged from the mold assembly, creating a potential electrical short out. Moreover, the bus bars are sometimes deflected inwardly between the spaced support points to interrupt the flow of electric current between the probes and bus bars.